Group III nitride semiconductor materials, such as gallium nitride (GaN), have been heretofore used for the purpose of forming light-emitting parts of semiconductor light-emitting devices (semiconductor light-emitting diodes), such as short-wavelength visible Light-Emitting Diodes (LEDs) and Laser Diodes (LDs) (refer to JP-B SHO 55-3834). The expression “light-emitting part of a semiconductor light-emitting device” refers to a region that comprises a light-emitting layer formed of a semiconductor material capable of causing emission of light and a functional layer, such as a clad layer, that is attendant on the light-emitting layer. As one example of the semiconductor material used for the purpose of forming a light-emitting layer, gallium-indium nitride (GaXIn1-XN wherein 0≦X≦1) has been known (refer to JP-B SHO 55-3834).
The light-emitting part formed of a Group III nitride semiconductor is obtained by using sapphire (α-Al2O3 single crystal) (refer to JP-B SHO 55-3834) or silicon single crystal (silicon) (refer to JP-A SHO 49-122294) as a substrate. On the occasion of forming a Group III nitride semiconductor layer on this substrate, the practice of interposing a buffer layer between these layers with a view to relaxing the lattice mismatch possibly occurring in their interface has been finding general acceptance (refer to JP-A SHO 60-173829). For example, a technique of utilizing a boron phosphide (BP) layer as a buffer layer for the purpose of forming a Group III nitride semiconductor layer on a silicon substrate has been known (refer to JP-A HEI 4-084486).
As means to form a silicon carbide layer as a buffer layer on a silicon substrate, a technique that resides in carbonizing the surface of the silicon substrate has been disclosed (refer to J. Electrochem. Soc. (U.S.A.), Vol. 137, No. 3, 1990, pp. 989-992). It is reported that, on the silicon carbide layer disposed on the surface of a silicon substrate, an aluminum-gallium-indium nitride (AlGaInN) layer of superior quality can be formed (refer to JP-A HEI 4-223330). It is, therefore, inferred that the formation on this layer of a functional layer, such as a Distributed Bragg Reflector (DBR), with the superlattice structure of a Group III nitride semiconductor layer is feasible.
Meanwhile, an example of the conventional technique that forms the DBR layer with a superlattice structure of GaN and AlN where sapphire is used as a substrate has been disclosed (refer to Appl. Phys. Lett. (U.S.A.), Volume 74, No. 7, 1999, pp. 1036-1038).
An attempt to dispose a superlattice structure where an AlN layer stacked on a silicon carbide buffer layer, for example, is used as an under layer entails the problem that the superlattice structure cannot be stably formed so long as this structure is formed of the combination of a GaN thin film and an AlN thin film, which are both Group III nitride semiconductor layers. This is because the GaN thin film possessing a flat surface destitute of pits and exhibiting continuity uniquely oriented toward a specific crystal direction cannot be formed as joined to the AlN thin film due to the condensation of Ga on the AlN film
In the case of disposing the superlattice structure formed of Group III nitride semiconductor layers via a silicon carbide buffer layer formed on a silicon substrate as described above, the conventional technique entails the problem that it is incapable of forming this superlattice structure from the Group III nitride semiconductor layers possessing continuity and exhibiting orderly orientation and further incapable of improving the light-emitting property of the semiconductor light-emitting diode.
This invention has been proposed with a view to overcoming the problems encountered by the conventional technique as described above and is aimed at providing a semiconductor light-emitting diode that enables the DBR film formed of a superlattice structure to excel in reflectance and acquire an improved light-emitting property.